1. Field of Invention
This invention pertains to the art of measuring lap joints between sheets of material, and most particularly to the art of rubber processing, such as tire building, where the length of such lap joint is important.
2. Description of Related Art
It is commonly known in the tire building industry to connect discrete sheets of material together via the use of a lap joint. Often, such lap joints are used with elastomeric tire components, such as liners or can also be used with reinforced components such as carcass plys or belts. Because a tire contains air at elevated pressures and undergoes rigorous use conditions, it is important that the lap joint holding portions of the tire together be secure. In order for the lap joint to be secure, the length of the lap joint must be sufficient such that the lap joint does not open, thereby releasing air to the atmosphere and deflating the tire. At the same time, if the lap joint is too large, having too large of a length, an undulation may appear in the tire's side wall. In addition, the cost of the tire goes up due to the increased amount of material with no corresponding increase in performance or benefit to the customer.
For this reason, in the process of manufacturing tire components, large sheets of liner compound, ply compound and the like are manufactured and carefully cut into proper lengths for the particular tire involved. During the tire manufacturing process, the individual sheets are attached to one another through a lap joint.
It has long been a need in the tire industry to develop an economical and accurate way of measuring and verifying the correct length of a lap joint. Although this need has been long recognized, to date, no economical automatic method has been developed. Instead, the inspection of a lap joint is typically made by a human tire builder as a tire is manufactured.
The present invention contemplates a new and improved method and apparatus of detecting and measuring the length of a lap joint. This method and apparatus is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.